The present invention relates to an exhaust gas recirculation system of an internal combustion engine, and more specifically to orifices disposed in a passage for recirculating the exhaust gas.
Unburnt carbon or other substances contained in the exhaust gas tend to stick to and deposit on an orifice disposed in an exhaust gas recirculation passage, and tend to decrease the opening size of the orifice with the passage of time. This undesired variation of the orifice opening size changes the amount of EGR and the distribution of the EGR gas among the cylinders of the engine, and badly affects exhaust emission control and engine performance.